Performance and Lesson for Study No.1, Op.60 by Fernando Sor (1778–1839). This is from my PDF or hardcopy sheet music or tab edition for classical guitar: 25 Progressive Studies, Op.60 by Fernando Sor.
Fernando Sor’s Op.60 is one of the most famous of all etude collections in the classical guitar repertoire. Each study covers a different pedagogical concept but the primary goal of the collection as a whole is the ability to play legato across various textures.
I would place this study around the grade 1 level. Here’s the YouTube Link for this lesson in case you want to watch it there.